To appreciate the advantages of the present invention, it is important to understand various aspects of how a typical internal combustion (IC) engine works.
In a typical IC engine, where the cylinders are fixed with respect to the engine frame, the motion of the connecting rods create side forces on their corresponding pistons that push against the cylinder walls. A standard four-cylinder internal combustion engine comprises four pistons, a crankshaft, and four connecting rods, each having a “big end” and a “small end.” Each piston is connected to the crankshaft through a corresponding connecting rod. The “big end” of the connecting rod is connected to one of several “rod journals” on the crankshaft—also known as a “crank throw”—that is offset from the “main journals” of the crankshaft. The “small end” of the connecting rod is pivotally attached to the piston via a “wrist pin.” As the piston reciprocates, the angle of the connecting rod with respect to the cylinder's longitudinal dimension changes. While the angular orientation of the connecting rod with respect to the piston is other than zero degrees, the connecting rod creates a side force on the piston against the cylinder wall. The magnitude of the force varies in relation to the angular orientation, gas pressures, and inertia forces.
To distribute these sideways forces, stabilize the path of the piston, and address friction issues, pistons are typically made with piston skirts that travel with the pistons inside the cylinders. While the pistons and skirts are likely lubricated to perform their role effectively, the larger the piston skirt, the greater a cross-sectional area of oil is sheared by the piston as it reciprocates. While a piston skirt performs an important function, its use creates an energy loss and thus decreases mechanical efficiency.
Furthermore, in a typical IC engine, while there is energy delivered by each piston to an output load through the crankshaft, a significant amount of energy is transferred through the crankshaft from each piston performing a power stroke to the pistons that are going through any of the three-non-powered strokes. Each piston cycles through a sequence of four strokes—the intake stroke (which is a forward or piston-extending stroke), the compression stroke (a return or piston-retracting stroke), the power stroke (another forward or piston-extending stroke), and the exhaust stroke (another return or piston-retracting stroke). At any given time while the engine is running, there is one cylinder performing a power stroke, another cylinder performing an exhaust stroke, another performing an intake stroke, and another a compression stroke. Because work must be performed to move each of the three pistons on non-powered strokes, the energy necessary to move them must be delivered by the piston performing the power stroke (excluding energy stored through inertia). In a standard in-line four-cylinder engine, this energy is delivered through the crankshaft.
The use of the crankshaft in a typical IC engine to transfer these between-cylinder forces and connect the cylinders to a common load increases the strength, size and rigidity requirements of the crankshaft as well as the size and number of bearing journals. Because the crankshaft is performing the dual roles of (1) transfering energy between the cylinders and (2) connecting the cylinders to a common load, the standard engine configuration results in a loss of energy and decreases mechanical efficiency.
Furthermore, a typical four-cylinder IC engine has five main journals and four rod journals to accommodate the four connecting rods driven by the pistons. The cross-sectional oil shear area across each of these nine-or-more relatively large bearings traveling through 360 degrees of rotation, multiplied by the distance the bearings travel per crankshaft revolution, is significant, and results in a loss of energy and decreases mechanical efficiency.